Description
Description: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA. Diurnal and semi-diurnal variations, driven by solar forcing, are two
fundamental modes in the Earth's weather and climate system. Radio
occultation (RO) measurements from the six COSMIC satellites (Constellation
Observing System for Meteorology Ionosphere and Climate) provide rather
uniform global coverage with high vertical resolution, all-weather and
diurnal sampling capability. This paper analyzes the diurnal and
semi-diurnal variations of both temperature and refractivity from two-year
(2007–2008) COSMIC RO measurements in the troposphere and stratosphere. The
RO observations reveal both propagating and trapped vertical structures of
diurnal and semi-diurnal variations, including transition regions near the
tropopause where data with high vertical resolution are critical. In the
tropics the diurnal amplitude in refractivity decreases with altitude from a
local maximum in the planetary boundary layer and reaches the minimum around
14 km and then further increase amplitude in the stratosphere. The upward
propagating component of the migrating diurnal tides in the tropics is
clearly captured by the GPS RO measurements, which show a downward
progression in phase from upper troposphere to the stratopause with a
vertical wavelength of about 25 km. Below 500 hPa (~5.5 km), seasonal
variations of the peak diurnal amplitude in the tropics follow the solor
forcing change in latitude, while at 30 km the seasonal pattern reverses
with the diurnal amplitude peaking at the opposite side of the equator
relative to the solar forcing. Polar regions shows large diurnal variations
in the stratosphere with strong seasonal variations and the cause(s) of
these variations require further investigations.